Carbon and carbon-containing nanotubes are unique carbon-based, molecular structures that exhibit interesting and useful electrical properties. There are two general types of carbon nanotubes, referred to as multi-walled carbon nanotubes (MWNTs) and single-walled carbon nanotubes (SWNTs). SWNTs have a cylindrical sheet-like, one-atom-thick shell of hexagonally-arranged carbon atoms, and MWNTs are typically composed of multiple coaxial cylinders of ever-increasing diameter about a common axis. Thus, SWNTs can be considered to be the structure underlying MWNTs and also carbon nanotube ropes, which are uniquely-arranged arrays of SWNTs.
Due to their unique electrical properties, carbon nanotubes are being studied for development, and in some instances, implemented, in a variety of applications. These applications include, among others, chemical and bio-type sensing, field-emission sources, selective-molecule grabbing, nano-electronic devices, and a variety of composite materials with enhanced mechanical and electro-mechanical properties. More specifically, for example, in connection with chemical and biological detection, carbon nanotubes are being studied for applications including medical devices, environmental monitoring, medical/clinical diagnosis and biotechnology for gene mapping and drug discovery. For general information regarding carbon nanotubes, and for specific information regarding SWNTs and related applications, reference may be made generally to the above-mentioned patent document and also to: “Carbon Nanotubes: Synthesis, Structure, Properties and Applications,” M. S. Dresselhaus, G. Dresselhaus and Ph. Avouris (Eds.), Springer-Verlag Berlin Heidelberg, New York, 2001; and “T. Single-shell Carbon Nanotubes of 1-nm Diameter,” Iijima, S. & Ichihashi, Nature 363, 603-605 (1993).
In some instances, the growth of SWNTs involves the formation of catalytic sites for growing carbon nanotubes, which can be accomplished using a variety of approaches. One such approach involves the use of an iron (Fe) containing catalyst supported on aluminum oxide type materials. While SWNTs can be readily grown using this approach, the catalytic regions on the substrate are often unclean. In addition, SWNTs grown from relatively dirty catalytic sites (e.g., with mound-like patterned alumina particles) can sometimes exhibit undesirable characteristics with the SWNTs themselves or for the implementations and processes in which the SWNTs are involved. For instance, when using atomic force microscopy (AFM) for the evaluation and/or processing of SWNTs grown in this manner, the AFM imaging tip can frequently pick up dirt particles. Catalyst supported on powders can also be challenging to implement due to difficulties associated with controlling individual catalytic nanoparticle size and in the patterning of nanoparticles at smaller scales (e.g., less than about 1 μm).
These and other factors have presented challenges to the large-scale production of carbon nanotubes, such as large arrays of nanotubes on full four-inch wafers.